The present invention concerns an adhesive for dentine, and relates more particularly to an adhesive particularly efficacious for the dentin of a tooth, which makes use of a primer characterized by containing a metal salt.
In dental therapy, the bond strength of the body, especially, dentin of a tooth with respect to other materials such as polymers, metals or porcelains must be increased. To this end, various forms of adhesives have already been proposed in the art.
Such dental adhesives are represented by:
an adhesive composition comprising (1) a radically polymerizable methacrylate monomer, (2) a mixture of benzoyl peroxide and an aromatic tertiary amine with or without a sulfinic acid salt, which serves as a polymerization catalyst and (3) a filler,
or an adhesive composition comprising (1) a radically polymerizable methacrylate monomer, (2) a photopolymerization initiator comprising camphor quinone serving as a photosensitizer and an amine acting as a reducing agent, such as N,N-dimethylaminoethyl methacrylate, and (3) a filler, and
an adhesive composition comprising (1) a radically polymerizable methacrylate monomer, (2) 4-methacryloyloxyethoxycarbonyl phthalic anhydride (4-META) which serves as an adhesionaccelerating monomer, and (3) a partial oxide of tributyl borane (TBBO) acting as a polymerization catalyst and PMMA serving as a filler.
In conventional adhesive compositions known so far in the art, various compounds are used as the polymerization initiators for radically polymerizable monomers. However, no sufficient bond strength is obtained with the exception of the use of TBBO. In order to better adhesion, it has been put forth to use adhesion-promoting monomers or monomers showing an affinity for dentin, e.g., carboxyl group-containing monomers such as 4-methacryloyloxyethoxycarbonyl phthalic acid (4-MET) or its anhydride (4-META) and 10-methacryloyloxydecyl malonic acid (MAC-10) and phosphoric acid group-containing monomers such as 10-methacryloyloxydecyl dihydrogen phosphate, but none of them are well effective for dentin.
Among conventional adhesives, TBBO-based systems are excellent, but a problem associated with the system is that TBBO must be used in large amounts, say 10% or more relative to the monomer only to obtain slow curing. Another problem is that they are allowed to be used substantially with a methyl methacrylate monomer alone; that is, they cannot be used in combination with dimethacrylates. In addition, the pre-treatment of dentin presents a clumsy problem that enamel have to be pretreated with phosphoric acid and dentin have to be pretreated with a citric acid solution containing ferric chloride, respectively. In order to overcome such problems inherent in TBBO, it is required to elaborate different polymerization initiation system. Benzoyl peroxide/aromatic tertiary amine/sulfinic acid salt-based initiators are considered effective for bonding to a dentin, but such available methods as set forth in Japanese Patent publication Nos. 56-33363 and 59-15468 fail to provide a sufficient bond strength to a dentin.
Apart from what has been described, it has been found that (thio) barbituric acid derivative/copper salt/chlorine ion-based initiators are considerably effective for bonding to a dentin--see for instance "Dental Material And Equipment", Vol. 8, Special Edition No. 14, pp. 89-90 (1989). However, they offers the same clumsy problem as is with the case of TBBO. Nor is any sufficient bond strength obtained; there is left much to be desired in this regard.